Conformations of n-alkyl-α/β-d-glucopyranoside surfactants: Impact on molecular properties

Abstract

Sugar-based surfactants are amphiphilic compounds bearing a head group derived from sugar. Such surfactants represent a good alternative to petroleum-based surfactants, because they can be prepared from bioproducts and generally have a low toxicity. The conformational flexibility of sugars is well known and since they can form competitive intramolecular hydrogen bonding-like interactions, the most stable conformations are often non-trivial. Calculating molecular descriptors in the context of Quantitative Structure-Property Relationship (QSPR) studies require relevant conformations. To find such conformations and then develop QSPR models, in this study, we carried out a conformational analysis of two anomers, octyl α-d-glucopyranoside and octyl β-d-glucopyranoside, to exhibit the main conformational parameters of glucopyranosides and their influence on some quantum chemical molecular descriptors that could be used in QSPR models of surfactants. From a starting set of 26 conformations for each anomer, optimized at B3LYP/6-31+G(d, p) level of Density Functional Theory, three most significant conformations, common for both glucopyranosides, generated by changing a single dihedral angle, were highlighted as the most significant conformations. The influence of solvent modeled by an implicit solvation model on conformations was discussed. Moreover, the influence of conformations on calculated molecular properties (partial charges, polarisability, and dipole moment) was discussed, for n-alkyl α/β-d-glucopyranosides. It was shown that for the studied alkyl glucosides, the dipole moment is influenced by the choice of conformations, but that the polarisability and the partial charges are less so.